Field of the Invention
This invention relates to the technical field of optics, and in particular, it relates to a light source and illumination device.
Description of the Related Art
Currently, multi-color semiconductor light sources are used more and more widely in stage lighting, decorative lighting and other fields. However, in actual products, because each color of the multi-color semiconductor light sources is generated separately by individual semiconductor chips, there is often a problem of non-uniform color mixing.
Japanese patent JP2006155956, Chinese patent 200810045644 and CN 102155713 respectively disclose the optical structures of multi-color semiconductor light sources. In such optical structures, light emitting diode (LED) chips of different colors together form a planar array, and above each LED is a corresponding collimator for collimating the light from the LED. The light from the LED, after collimation by the collimators, are incident on a fly-eye lens to make the light from different color LEDs uniform.
In another approach disclosed in Chinese patent CN101988631, a set of dichroic filters combine lights from different color LED arrays using wavelength-based combination, where the light from each LED array is the same color. Compared to the earlier mentioned approach, this approach has the advantage of small etendue, but a shortcoming is that it can only combine monochromatic lights with no wavelength overlap, and cannot combined wide-band light such as white light. Also, this approach is relatively costly due to the use of dichroic filters.
In the approach where LEDs of different colors together form a planar array, how to minimize the etendue of the light source is a key factor in controlling the brightness of the light source. However, in conventional technologies, the etendue of light sources is not optimized.
The packaging structure of a conventional LED chip is shown in FIG. 11. The LED chip 1101 is mounted on a heat conducting substrate 1102, and a silicone lens 1103 having an arc shaped exterior is used to seal the LED chip 1101 and to further enhance the light extraction efficiency of the LED chip. The silicone lens 1103 can increase the total luminous flux emitted by the LED by 20-30%, but at the same time also increases its etendue by 2-2.5 times (refer to equation (2) in the descriptions later). Therefore, the emission brightness, i.e. the ratio of the total luminous flux and the etendue, is significantly reduced by the use of the silicone lens 1103. In applications that do not have a requirement on the etendue, such as general illumination, the packaging structure shown in FIG. 11 is adequate, because it can obtain higher output luminous flux; however, for applications that require limited etendue such as projection light and stage light that requires specific light spot sizes, this type of packaging structure will significantly reduce the ultimate emission brightness.
On the other hand, a commonly used collimating device is shown in FIG. 12 as item 1201. This collimating device is typically referred to as a total internal reflection (TIR) lens, and its principle is to use refraction by the center curved surface 1201a and total reflection by the surrounding side call 1201b to collimate the light of the LED. An advantage of this type of collimating device is that it can collect light emitted at all angles, but its shortcoming is that it can cause the etendue of the output light to be far greater than the etendue of the light source, which significantly reduces the light emission brightness.